In process control systems for controlling process variables, such as temperatures, pressures, and the like, the systems are based on the combinations of single actuators with single controlled variables PV, such as, for example, a single heater, a single temperature sensor, and a single temperature controller for a case wherein it is the temperature that is subject to control.
On the other hand, a method for controlling temperature has also been proposed wherein two actuators, specifically a heating actuator (a heater) and a cooling actuator (a cooler) are operated cooperatively. See, for example, Japanese Patent No. 3805957 (“the JP '957”). FIG. 10 is a diagram illustrating an example of the application, to temperature control of a heat treatment furnace, of a controlling device as disclosed in the JP '957, and FIG. 11 is a block diagram illustrating the structure of a controlling device disclosed in the JP '957. The heat treatment furnace 100 circulates air that is heated by the heater 101 and cooled by the cooler 102.
The controller 104 calculates an operating variable MV_A for heating through a PID control calculation based on a controlled variable (a temperature measurement value) PV_A that is measured by a temperature sensor 103 within the heat treatment furnace 100, and based on a setting value SP_A. A controller 105 uses a desirable value for the heating operating variable MV_A of the controller 104 as a setting value SP_B, and uses the heating operating variable MV_A of the controller 104 as a controlled variable to calculate an operating variable MV_B for cooling, through a PID control calculation.
The technology disclosed in the JP '957 can improve energy efficiency by reducing offsetting of heating with cooling, rather than simply controlling the temperature. The distinctive feature of the technology disclosed in the JP '957 is the addition of a control loop that makes adjustments while constantly monitoring the heater output (the operating variable MV_A) while focusing on the equilibrium between the heater output and the cooler output, which is a factor that has an impact on energy efficiency.
The technology disclosed in the JP '957 is a control technology that assumes a combination of a single cooling system (a single cooling actuator) with a single heating system (a single heating actuator). However, the actuators that effect the energy efficiency are not necessarily limited to two actuators. For example, as illustrated in FIG. 12, a plurality of zones 106-1 through 106-4 that are to be heated in the heat treatment furnace 100 and a heater 101-1 through 101-4 may be provided for each individual zone 106-1 through 106-4, and, further, a single cooling device 102 may be provided for cooling the air within the heat treatment furnace 100, that is, a single cooling system may be combined with a plurality of heating systems.
In the structure in FIG. 12, if there is a plurality of normal control systems for the purpose of heating, these can control a plurality of controlled variables (temperatures), so the structure is one that can run without problems, insofar as energy efficiency is not taken into account. Moreover, from the perspective of manufacturing cost of the manufacturing equipment, this structure is actually a reasonable structure. In this way, it is not possible to apply the technology that is disclosed in the JP '957 to a configuration wherein there is a plurality of primary control systems for the primary purpose of control with only a single secondary control system for adjusting the equilibrium point that is the desired operating variable output when the primary control is in a study state.
The present invention is to solve the problem set forth above, and an aspect thereof is to provide a cooperative operating device and method able to achieve energy conservation in a multi-loop control system that has a plurality of primary control systems for the purpose of primary control and only a single secondary control system for controlling an equilibrium point that is a desirable operating variable output with the primary control in a steady state.